Enhanced etch and deposition profile control using plasma sheath engineering

ABSTRACT

A plasma processing tool is used to deposit material on a workpiece. For example, a method for conformal deposition of material is disclosed. In this embodiment, the plasma sheath shape is modified to allow material to impact the workpiece at a range of incident angles. By varying this range of incident angles over time, a variety of different features can be deposited onto. In another embodiment, a plasma processing tool is used to etch a workpiece. In this embodiment, the plasma sheath shape is altered to allow ions to impact the workpiece at a range of incident angles. By varying this range of incident angles over time, a variety of differently shaped features can be created.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is divisional of prior U.S. application Ser. No.12/645,638, filed Dec. 23, 2009, which itself is a continuation in part(CIP) of U.S. application Ser. No. 12/644,103, filed Dec. 22, 2009, nowU.S. Pat. No. 8,101,510, which itself is a continuation in part (CIP) ofU.S. application Ser. No. 12/418,120, filed Apr. 3, 2009, thedisclosures of which are incorporated herein by reference.

This application is also related to U.S. application Ser. No. 12/417,929filed Apr. 3, 2009, now U.S. Pat. No. 7,767,977, which is incorporatedherein by reference.

FIELD

This disclosure relates to plasma processing, and more particularly to aplasma processing apparatus.

BACKGROUND

A plasma processing apparatus generates a plasma in a process chamberfor treating a workpiece supported by a platen in the process chamber. Aplasma processing apparatus may include, but not be limited to, dopingsystems, etching systems, and deposition systems. The plasma isgenerally a quasi-neutral collection of ions (usually having a positivecharge) and electrons (having a negative charge). The plasma has anelectric field of about 0 volts per centimeter in the bulk of theplasma. In some plasma processing apparatus, ions from the plasma areattracted towards a workpiece. In a plasma doping apparatus, ions may beattracted with sufficient energy to be implanted into the physicalstructure of the workpiece, e.g., a semiconductor substrate in oneinstance.

The plasma is bounded by a region proximate the workpiece generallyreferred to as a plasma sheath. The plasma sheath is a region that hasfewer electrons than the plasma. The light emission from this plasmasheath is less intense than the plasma since fewer electrons are presentand hence few excitation-relaxation collisions occur. Hence, the plasmasheath is sometimes referred to as “dark space.”

Turning to FIG. 1, a cross sectional view of portions of a known plasmaprocessing apparatus is illustrated where a plasma 140 has a plasmasheath 142 adjacent to a front surface of a workpiece 138 to be treated.The front surface of the workpiece 138 defines a plane 151, and theworkpiece 138 is supported by a platen 134. The boundary 141 between theplasma 140 and the plasma sheath 142 is parallel to the plane 151. Ions102 from the plasma 140 may be attracted across the plasma sheath 142towards the workpiece 138. Accordingly, the ions 102 that areaccelerated towards the workpiece 138 generally strike the workpiece 138at about a 0° angle of incidence relative to the plane 151 (e.g.,perpendicular to the plane 151). There can be a small angular spread ofthe angle of incidence of less than about 3°. In addition, bycontrolling plasma process parameters such as gas pressure within aprocess chamber, the angular spread may be increased up to about 5°.

A drawback with conventional plasma processing is the lack of angularspread control of the ions 102. As structures on the workpiece becomesmaller and as three dimensional structures become more common (e.g.,trench capacitors, vertical channel transistors such as FinFETs) itwould be beneficial to have greater angle control. For example, a trench144 having an exaggerated size for clarity of illustration is shown inFIG. 1. With ions 102 being directed at about a 0° angle of incidence oran even angular spread up to 5°, it can be difficult to uniformly treatthe sidewalls 147 of the trench 144.

Accordingly, there is a need for a plasma processing apparatus whichovercomes the above-described inadequacies and shortcomings.

SUMMARY

The problems of the prior art are overcome by the methods of plasmaprocessing disclosed herein. In certain embodiments, a plasma processingtool is used to deposit material on a workpiece. For example, a methodfor conformal deposition of material is disclosed. In this embodiment,the plasma sheath shape is modified to allow material to impact theworkpiece at a range of incident angles. By varying this range ofincident angles over time, a variety of different features can bedeposited onto. In another embodiment, a plasma processing tool is usedto etch a workpiece. In this embodiment, the plasma sheath shape isaltered to allow ions to impact the workpiece at a range of incidentangles. By varying this range of incident angles over time, a variety ofdifferently shaped features can be created.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present disclosure, reference is madeto the accompanying drawings, in which like elements are referenced withlike numerals, and in which:

FIG. 1 is a simplified block diagram of a conventional plasma processingapparatus consistent with the prior art;

FIG. 2 is a block diagram of a plasma processing apparatus consistentwith an embodiment of the disclosure;

FIG. 3 is a block diagram of a plasma doping apparatus consistent withan embodiment of the disclosure;

FIG. 4 is a cross sectional view of a pair of insulators to control ashape of a boundary between a plasma and a plasma sheath;

FIG. 5 is a cross sectional view consistent with FIG. 4 illustrating iontrajectories of ions accelerated across the boundary of FIG. 4;

FIG. 6 is a plot of angular ion distributions of the ion trajectories ofFIG. 5;

FIG. 7 is a block diagram of a system to control a vertical spacingbetween a pair of insulators and a workpiece;

FIG. 8 is a cross sectional view consistent with FIG. 7 illustrating iontrajectories at differing vertical spacing;

FIG. 9 is a block diagram of a system to control a horizontal spacingbetween a pair of insulators;

FIG. 10 is a cross sectional view consistent with FIG. 9 to illustratingion trajectories at differing horizontal spacing;

FIG. 11 is a block diagram of a plasma processing apparatus having ascanning system to move a pair of insulating sheets relative to aworkpiece;

FIG. 12 is a plan view of the insulating sheets of FIG. 11 showingrelative movement between the insulating sheets and a disk shapedworkpiece;

FIG. 13 is a block diagram of a scanning system consistent with FIG. 11having a plurality of insulators;

FIG. 14 is a block diagram of a plasma processing apparatus consistentwith a second embodiment of the disclosure;

FIG. 15 is a cross sectional view of two insulators used to control ashape of a boundary between a plasma and a plasma sheath;

FIG. 16 is a plot of angular ion distributions of the ion trajectoriesof FIG. 15;

FIG. 17 is a block diagram of a system to control a vertical spacingbetween a set of insulators and a workpiece;

FIG. 18 is a cross sectional view consistent with FIG. 17 illustratingion trajectories at a first vertical spacing;

FIG. 19 is a cross sectional view consistent with FIG. 17 illustratingion trajectories at a second vertical spacing;

FIG. 20 is a block diagram of a system to control a horizontal spacingbetween insulators;

FIG. 21 is a cross sectional view consistent with FIG. 20 toillustrating ion trajectories at negative horizontal spacing;

FIG. 22 is a cross sectional view of three insulators used to control ashape of a boundary between a plasma and a plasma sheath;

FIG. 23 is a plot of angular ion distributions of the ion trajectoriesof FIG. 22;

FIGS. 24 a-c are cross sectional views of additional embodiments of theinsulating modifier;

FIG. 25 is a block diagram of a plasma processing apparatus having ascanning system to move insulating sheets relative to a workpiece;

FIG. 26 is a plan view of the insulating sheets of FIG. 25 showingrelative movement between the insulating sheets and a disk shapedworkpiece;

FIG. 27 is a block diagram of a scanning system consistent with FIG. 25having a plurality of insulators;

FIG. 28 a illustrates the traditional path of ions from a plasma to aworkpiece;

FIG. 28 b illustrates the conformal deposition of a narrow threedimensional feature;

FIG. 28 c illustrates the conformal deposition of a wide, shallow threedimensional feature;

FIG. 29 a shows the ion angular distribution associated with FIG. 28 a;

FIG. 29 b shows the ion angular distribution associated with FIG. 28 b;

FIG. 29 c shows the ion angular distribution associated with FIG. 28 c;

FIGS. 30 a-f show the effects of various angles of incidence ondeposition;

FIG. 31 a illustrates the depositing of material with an air gap in athree dimensional feature;

FIG. 31 b shows the ion angular distribution associated with FIG. 30 a;

FIG. 32 a illustrates the etching of a three-dimensional feature withvertical sidewalls;

FIG. 32 b illustrates the etching of a three-dimensional feature withinwardly tapered sidewalls;

FIG. 32 c illustrates a feature shape that can be created using the ionangular distribution of FIG. 29 b;

FIG. 32 d illustrates a feature shape that can be created using the ionangular distribution of FIG. 29 c;

FIG. 33 a illustrates the etching of a three-dimensional feature withoutwardly tapered sidewalls;

FIG. 33 b illustrates a feature shape that can be created using the ionangular distribution of FIG. 30 b;

FIG. 33 c illustrates a feature shape that can be created using the ionangular distribution of FIG. 30 b; and

FIG. 33 d illustrates a feature shape that can be created using the ionangular distribution of FIG. 30 b.

DETAILED DESCRIPTION

FIG. 2 is a block diagram of one plasma processing apparatus 200 havingan insulating modifier 208 consistent with an embodiment of thedisclosure. The insulating modifier 208 is configured to modify anelectric field within the plasma sheath 242 to control a shape of aboundary 241 between the plasma 140 and the plasma sheath 242.Accordingly, ions 102 that are attracted from the plasma 140 across theplasma sheath 242 may strike the workpiece 138 at a range of incidentangles.

The plasma processing apparatus 200 may be further described herein as aplasma doping apparatus. However, the plasma processing apparatus 200may also include, but not be limited to, etching and deposition systems.Furthermore, a plasma doping system can perform many differing materialmodification processes on a treated workpiece. One such process includesdoping a workpiece, such as a semiconductor substrate, with a desireddopant.

The plasma processing apparatus 200 may include a process chamber 202, aplaten 134, a source 206, and the insulating modifier 208. The platen134 is positioned in the process chamber 202 for supporting theworkpiece 138. The workpiece may include, but not be limited to, asemiconductor wafer, flat panel, solar panel, and polymer substrate. Thesemiconductor wafer may have a disk shape with a diameter of 300millimeters (mm) in one embodiment. The source 206 is configured togenerate the plasma 140 in the process chamber 202 as is known in theart. In the embodiment of FIG. 2, the insulating modifier 208 includes apair of insulators 212 and 214 defining a gap there between having ahorizontal spacing (G). In other embodiments, the insulating modifiermay include only one insulator. The pair of insulators 212 and 214 maybe a pair of sheets having a thin, flat shape. In other embodiments, thepair of insulators 212 and 214 may be other shapes such as tube shaped,wedge shaped, and/or have a beveled edge proximate the gap.

In one embodiment, the horizontal spacing of the gap defined by the pairof insulators 212 and 214 may be about 6.0 millimeters (mm). The pair ofinsulators 212 and 214 may also be positioned a vertical spacing (Z)above the plane 151 defined by the front surface of the workpiece 138.In one embodiment, the vertical spacing (Z) may be about 3.0 mm.

In operation, a gas source 288 supplies an ionizable gas to the processchamber 202. Examples of an ionizable gas include, but are not limitedto, BF₃, BI₃, N₂, Ar, PH₃, AsH₃, B₂H₆, H₂, Xe, Kr, Ne, He, SiH₄, SiF₄,GeH₄, GeF₄, CH₄, CF₄, AsF₅, PF₃, and PF₅. The source 206 may generatethe plasma 140 by exciting and ionizing the gas provided to the processchamber 202. Ions may be attracted from the plasma 140 across the plasmasheath 242 by different mechanisms. In the embodiment of FIG. 2, thebias source 290 is configured to bias the workpiece 138 to attract ions102 from the plasma 140 across the plasma sheath 242. The bias source290 may be a DC power supply to provide a DC voltage bias signal or anRF power supply to provide an RF bias signal.

Advantageously, the insulating modifier 208 modifies the electric fieldwithin the plasma sheath 242 to control a shape of the boundary 241between the plasma 140 and the plasma sheath 242. In the embodiment ofFIG. 2, the insulating modifier 208 includes a pair of insulators 212and 214. The insulators 212, 214 may be fabricated of quartz, alumina,boron nitride, glass, silicon nitride, etc. The boundary 241 between theplasma 140 and the plasma sheath 242 may have a convex shape relative tothe plane 151. When the bias source 290 biases the workpiece 138, ions102 are attracted across the plasma sheath 242 through the gap betweenthe insulators 212 and 214 at a large range of incident angles. Forinstance, ions following trajectory path 271 may strike the workpiece138 at an angle of +θ° relative to the plane 151. Ions followingtrajectory path 270 may strike the workpiece 138 at about an angle of 0°relative to the same plane 151. Ions following trajectory path 269 maystrike the workpiece 138 an angle of −θ° relative to the plane 151.Accordingly, the range of incident angles may be between +θ° and −θ°centered about 0°. In addition, some ion trajectories paths such aspaths 269 and 271 may cross each other. Depending on a number of factorsincluding, but not limited to, the horizontal spacing (G) between theinsulators 212 and 214, the vertical spacing (Z) of the insulators abovethe plane 151, the dielectric constant of the insulators 212 and 214,and other plasma process parameters, the range of incident angles (θ)may be between +60° and −60° centered about 0°. Hence, small threedimensional structures on the workpiece 138 may be treated uniformly bythe ions 102. For example, the sidewalls 247 of the trench 244 having anexaggerated size for clarity of illustration may be more uniformlytreated by the ions 102 compared to that of FIG. 1.

Turning to FIG. 3, a block diagram of one exemplary plasma dopingapparatus 300 is illustrated. Consistent with the apparatus of FIG. 2,the plasma doping apparatus 300 has the pair of insulators 212 and 214to control a shape of the boundary 241 between the plasma 140 and theplasma sheath 242. The plasma doping apparatus 300 includes a processchamber 202 defining an enclosed volume 303. A gas source 304 provides aprimary dopant gas to the enclosed volume 303 of the process chamber 302through the mass flow controller 306. A gas baffle 370 may be positionedin the process chamber 202 to deflect the flow of gas from the gassource 304. A pressure gauge 308 measures the pressure inside theprocess chamber 202. A vacuum pump 312 evacuates exhausts from theprocess chamber 202 through an exhaust port 310. An exhaust valve 314controls the exhaust conductance through the exhaust port 310.

The plasma doping apparatus 300 may further includes a gas pressurecontroller 316 that is electrically connected to the mass flowcontroller 306, the pressure gauge 308, and the exhaust valve 314. Thegas pressure controller 316 may be configured to maintain a desiredpressure in the process chamber 202 by controlling either the exhaustconductance with the exhaust valve 314 or a process gas flow rate withthe mass flow controller 306 in a feedback loop that is responsive tothe pressure gauge 308.

The process chamber 202 may have a chamber top 318 that includes a firstsection 320 formed of a dielectric material that extends in a generallyhorizontal direction. The chamber top 318 also includes a second section322 formed of a dielectric material that extends a height from the firstsection 320 in a generally vertical direction. The chamber top 318further includes a lid 324 formed of an electrically and thermallyconductive material that extends across the second section 322 in ahorizontal direction.

The plasma doping apparatus further includes a source 301 configured togenerate a plasma 140 within the process chamber 202. The source 301 mayinclude a RF source 350 such as a power supply to supply RF power toeither one or both of the planar antenna 326 and the helical antenna 346to generate the plasma 140. The RF source 350 may be coupled to theantennas 326, 346 by an impedance matching network 352 that matches theoutput impedance of the RF source 350 to the impedance of the RFantennas 326, 346 in order to maximize the power transferred from the RFsource 350 to the RF antennas 326, 346.

The plasma doping apparatus may also include a bias power supply 390electrically coupled to the platen 134. The plasma doping system mayfurther include a controller 356 and a user interface system 358. Thecontroller 356 can be or include a general-purpose computer or networkof general-purpose computers that may be programmed to perform desiredinput/output functions. The controller 356 may also includecommunication devices, data storage devices, and software. The userinterface system 358 may include devices such as touch screens,keyboards, user pointing devices, displays, printers, etc. to allow auser to input commands and/or data and/or to monitor the plasma dopingapparatus via the controller 356. A shield ring 394 may be disposedaround the platen 134 to improve the uniformity of implanted iondistribution near the edge of the workpiece 138. One or more Faradaysensors such as Faraday cup 399 may also be positioned in the shieldring 394 to sense ion beam current.

In operation, the gas source 304 supplies a primary dopant gascontaining a desired dopant for implantation into the workpiece 138. Thesource 301 is configured to generate the plasma 140 within the processchamber 302. The source 301 may be controlled by the controller 356. Togenerate the plasma 140, the RF source 350 resonates RF currents in atleast one of the RF antennas 326, 346 to produce an oscillating magneticfield. The oscillating magnetic field induces RF currents into theprocess chamber 202. The RF currents in the process chamber 202 exciteand ionize the primary dopant gas to generate the plasma 140.

The bias power supply 390 provides a pulsed platen signal having a pulseON and OFF periods to bias the platen 134 and hence the workpiece 138 toaccelerate ions from the plasma 140 towards the workpiece 138 across theplasma sheath 242. The ions 102 may be positively charged ions and hencethe pulse ON periods of the pulsed platen signal may be negative voltagepulses with respect to the process chamber 202 to attract the positivelycharged ions 102. The frequency of the pulsed platen signal and/or theduty cycle of the pulses may be selected to provide a desired dose rate.The amplitude of the pulsed platen signal may be selected to provide adesired energy.

Advantageously, the pair of insulators 212 and 214 controls the shape ofthe boundary 241 between the plasma 140 and the plasma sheath 242 aspreviously detailed with respect to FIG. 2. Therefore, the ions 102 maybe attracted across the plasma sheath 242 through the gap between theinsulators 212 and 214 at a large range of incident angles for dopingthe workpiece 138.

Turning to FIG. 4, a partial cross sectional view of the pair ofinsulators 212 and 214 and workpiece 138 is illustrated showing theelectric field lines in the plasma sheath 242 about the gap defined bythe insulators 212 and 214. The electric field lines and resultingarcuate boundary 241 between the plasma and the plasma sheath 242resulted from a computer simulation with the workpiece 138 biased at−2,000 volts and the insulators 212 and 214 fabricated of glass. Asillustrated, the arcuate boundary 241 about the gap may further have aconvex shape relative to the plane 151.

FIG. 5 is a cross sectional view consistent with FIG. 4 illustratingsimulated ion trajectories accelerated across the plasma sheath 242through the gap between the insulators 212 and 214. In a plasma dopingapparatus, the ions may be implanted in the workpiece 138 in a centralarea of the gap spacing due to the shape of the boundary 241 and theelectric field lines within the plasma sheath 242. For instance, of thetotal horizontal spacing (G1) between the insulators 212 and 214, ionsstrike the workpiece 138 about the central horizontal spacing (G3). Noions strike the workpiece about the peripheral horizontal spacing (G2)and (G4) proximate the insulators 212 and 214 in this embodiment.

FIG. 6 is a plot 602 of the distribution of incident angles of ionsstriking the workpiece 138 consistent with the illustrated iontrajectories of FIG. 5. As shown, the plot 602 reveals the incidentangles are centered about 0° and vary over a large range of angles fromabout +60° to −60°. This large range of incident angles enablesconformal doping of three dimensional structures. For example, thesidewalls of a trench structure may be more uniformly doped with ionshaving such a large range of incident angles.

Turning to FIG. 7, a block diagram of another embodiment consistent withthe present disclosure is illustrated where the vertical spacing (Z)between an insulating modifier and the plane 151 defined by the frontsurface of the workpiece 138 may be adjusted. The insulating modifiermay be the pair of insulators 212 and 214 as detailed in otherembodiments. An actuator 702 may be mechanically coupled to the pair ofinsulators 212 and 214 to drive the insulators in a vertical directionas shown by arrows 720, 722 relative to the plane 151. The Z position ofthe pair of insulators 212 and 214 relative to the plane 151, and alsorelative to each other, influences the shape of the boundary between theplasma and the plasma sheath and also the trajectories of the ionsstriking the workpiece 138. The actuator 702 may be controlled by acontroller such as controller 356.

FIG. 8 is a cross sectional view consistent with FIG. 7 to illustrateion trajectories at differing Z positions of the pair of insulators 212and 214 relative to the plane 151 with all other parameters being equal.In the first relatively short Z gap position 820, the insulators 212,214 are positioned a first distance (Z1) above the plane 151. In acomparatively taller Z gap position 840, the insulators 212, 214 arepositioned a second distance (Z2) above the plane 151, where (Z2)>(Z1).In the first position 820, the boundary 841 between the plasma and theplasma sheath has a convex shape relative to the plane 151. The boundary841 also has a shape that approximately approaches the shape of aportion of a circumference of a circle where an apex of the arcuateshape is a distance (Za) above a top surface of the insulator 212. Incontrast, the boundary 843 in the second position 840 has a shallowershape where the apex of the arcuate shape is a shorter distance (Zb)above the top surface of the insulator 212, or where (Zb)<(Za). Theshape of the boundaries 841, 843 combined with the Z gap distances (Z1)and (Z2) and the electric field lines in the plasma sheath, influencesthe angular spread of the ions striking the workpiece 138. For example,the angular spread of ions striking the workpiece 138 with therelatively short Z gap position 820 is greater than the angular spreadof ions striking the workpiece 138 with the relatively longer Z gapposition. In addition, ions strike a wider horizontal spacing (G5) ofthe workpiece 138 with the shorter Z gap position 820 compared to thehorizontal spacing (G6) with the taller Z gap position, where (G6)<(G5).Although not illustrated in FIG. 8, the Z gap positions of eachinsulator 212 and 214 may also be different from each other to furtherinfluence the shape of the boundary between the plasma and the plasmasheath and accordingly the angular spread of ions.

Turning to FIG. 9, a block diagram of another embodiment consistent withthe present disclosure is illustrated where the horizontal spacing (G)between insulators 212 and 214 may be adjusted. The horizontal spacingadjustments may in lieu of, or in addition to, the earlier detailedvertical spacing adjustments of FIGS. 8 and 9. An actuator 902 may bemechanically coupled to at least one of the pair of insulators 212 and214 to drive the insulators in the direction shown by the arrow 906relative to one another. The actuator 902 may be controlled by acontroller such as controller 356.

FIG. 10 is a cross sectional view consistent with FIG. 9 to illustrateion trajectories at differing horizontal gap spacing between theinsulators 212 and 214 with all other parameters being equal. In thefirst relatively shorter horizontal gap position 1020, the insulators212, 214 are positioned a first horizontal distance (Ga) from oneanother. In a comparatively longer horizontal gap position 1040, theinsulators 212, 214 are positioned a second horizontal distance (Gb)from each other, where (Gb)>(Ga). In the first position 1020, theboundary 1041 between the plasma and the plasma sheath has a convexshape relative to the plane 151. The boundary 1041 also has a shape thatapproximately approaches the shape of a portion of a circumference of acircle. In contrast, the boundary 1043 in the second position 1040 has aconvex shape relative to the plane 151 where a central portion of theboundary 1043 is about parallel to the plane 151. As a result, a largercorresponding central portion of the workpiece 138 is struck with ionshaving about a 0° angle of incidence relative to the plane 151.

FIG. 11 is a block diagram of a plasma processing apparatus 1100 havinga scanning system 1102 to drive an insulating modifier 208 relative theworkpiece 138. In the embodiment of FIG. 11, the insulating modifier 208includes a pair of square insulating sheets 1112 and 1114 that are bestseen in FIG. 12. The scanning system 1102 may include an actuator 1104mechanically coupled to the insulating sheets 1112 and 1114 to drive thesame. The actuator 1104 may be controlled by a controller such ascontroller 356.

FIG. 12 is plan view of the square insulating sheets 1112 and 1114 and adisk shaped workpiece 138 to illustrate one example of relative movementbetween the same. In the embodiment of FIG. 12, the scanning system 1102may drive the square insulating sheets 1112 and 1114 from Position A, toPosition B, and Position C, etc. so that all portions of the workpiece138 are exposed to the gap defined by the pair of square insulatingsheets 1112 and 1114. If a Cartesian coordinate system is defined asdetailed in FIG. 12, the insulating sheets 1112 and 1114 are driven inthe X direction of FIG. 12. In other embodiments, the insulating sheets1112 and 1114 or another set of different insulating sheets may bedriven in the Y direction or any angle between the X and Y directions.In addition, the workpiece 138 may be rotated as the scanning system1102 drives the insulating sheets 1112 and 1114 in one direction. Theworkpiece 138 may also be rotated by a predetermined rotation angleafter the scanning system 1102 drives the insulating sheets in onedirection. In one example, the rotation may be about a central axis ofthe workpiece as illustrated by arrow 1124.

Turning to FIG. 13, a scanning system 1102 consistent with FIG. 11 isillustrated. Compared to FIG. 11, the scanning system 1102 of FIG. 13includes a plurality of insulators 1302-1, 1302-2, 1302-3, . . .1302-(n−1), and 1302-n that define a plurality of gaps there between1303-1, 1303-2, . . . 1303-n. The scanning system may drive theplurality of insulators 1302-1, 1302-2, 1302-3, . . . 1302-(n−1), and1302-n relative to the workpiece 138 so the plurality of gaps 1303-1,1303-2, . . . 1303-n pass over the workpiece 138.

FIG. 14 shows a second embodiment of the plasma processing apparatus ofFIG. 2. As described above, the plasma processing apparatus 200 mayinclude a process chamber 202, a platen 134, a source 206, and theinsulating modifier 248. In the embodiment of FIG. 14, the insulatingmodifier 248 includes insulators 252 and 254 defining a gap therebetween having a horizontal spacing (G). In other embodiments, theinsulating modifier 248 may include only one insulator. In oneembodiment, the horizontal spacing of the gap defined by the insulators252 and 254 may be between about 1 and 60 millimeters (mm), depending onthe sheath thickness and the desired angular distribution.

The insulators 252 and 254 may also be positioned a vertical spacing(Z1,Z2) above the plane 151 defined by the front surface of theworkpiece 138. In one embodiment, the closer vertical spacing (Z1) maybe between about 1 and 10 mm. In some embodiments, the difference inheight between the insulators (i.e. Z2-Z1) may be between about 0 and 40mm, depending on the sheath thickness and the desired angulardistribution. While FIG. 14 shows insulator 252 at a greater verticalheight than insulator 254, the insulator 254 may have a greater verticalheight than insulator 252 if desired.

The difference in vertical height between the two insulators creates agap angle, relative to plane 151. The gap angle is measured by creatinga plane 257, which passes though the edges of insulator 252 closest tothe sheath and proximate the gap and the edges of insulator 254 closestto the sheath and proximate the gap. The angle between plane 257 andplane 151 defines the gap angle (ψ). In some embodiments, the gap width(δ) is measured along plane 257, rather than along the horizontal. Thegap width (δ) is related to the horizontal spacing (G) according to theequation:

δ=G/cos(ψ),

where ψ is the gap angle. The gap width (δ) may be between 0 and 40 mm.In some embodiments, the horizontal spacing may be 0 or even negative(which is achieved when the insulators overlap one another). A largedifference in Z2-Z1, coupled with a 0 mm or negative horizontal spacingcan be used to create very large center angles, such as greater than80°.

As will be described in more detail below, the disclosed apparatus canbe used to create angular distributions of ions. These angulardistributions, such as those shown in FIGS. 16 and 23, can becharacterized by two parameters. The first is the center angle, which isthe angle that forms the center of the angular distribution. The centerangle is defined as the angular deviation from the orthogonal to plane151. In other words, ions that strike perpendicular to the plane 151 atsaid to have a center angle of 0°. As the angle of incidence become moreparallel to plane 151, its value increases.

In FIG. 16, the center angle corresponds to about 45°. In FIG. 23, thereare two center angles, at −45° and +45°. The second parameter ofinterest is the angular spread, or angular range. This is thedistribution of ions about the center angle. In other words, all ions donot strike the workpiece at the same angle. Rather, they arrive havingan angular distribution about the center angle. In FIG. 16, thedistribution of angles is roughly from 35° to 55°; thereby having anangular spread (or range) of about 20°. Similarly, the angular spread(or angular distribution) of FIG. 23 is about 20°.

The gap angle (ψ) helps to define the center angle. To create a centerangle that is not perpendicular to the workpiece plane 151 (i.e. anon-zero center angle), the gap angle (ψ) may be non-zero. In otherwords, a non-zero gap angle (ψ) implies that the gap plane 257 is notparallel to the workpiece plane 151. By having a non-zero gap angle (ψ),the center angle is changed so as not to be perpendicular to theworkpiece plane 151. Larger gap angles (i.e. >30°) typically createlarger deviations in the center angle (i.e. >30°). Smaller gap angles(i.e. when the gap plane 257 and the workpiece plane 151 are nearlyparallel) produce smaller center angles (i.e. <10°).

The boundary 241 between the plasma 140 and the plasma sheath 242 mayhave an irregular shape relative to the plane 151. When the bias source290 biases the workpiece 138, ions 102 are attracted across the plasmasheath 242 through the gap between the insulators 252 and 254 at a largerange of center angles. For instance, ions may strike the workpiece 138at a non-zero center angle of +θ° relative to the plane 151. If thevertical spacing of the insulators is reversed, ions may strike theworkpiece 138 a non-zero center angle of −θ° relative to the plane 151.Accordingly, the range of incident angles may be centered about θ°,where θ is between −80° and 80°. Depending on a number of factorsincluding, but not limited to, the horizontal spacing (G) between theinsulators 252 and 254, the vertical spacing (Z1, Z2) of the insulatorsabove the plane 151, the gap width (δ), the gap angle (ψ), thedifference in vertical spacing (Z2-Z1), the dielectric constant of theinsulators 252 and 254, the dielectric thickness of the insulators 252and 254, and other plasma process parameters, the range and center ofthe incident angles (θ) may be modified. For example, the angulardistribution may be between +5 degrees and −5 degrees, while the centerangle can be between −80° and +80°. In other embodiments, the angulardistribution may be greater (or smaller). Similarly, the center anglecan be modified to achieve other values. Hence, small three dimensionalstructures on the workpiece 138 may be treated uniformly by the ions102.

FIG. 15 is a cross sectional view illustrating simulated iontrajectories accelerated across the plasma sheath 242 through the gapbetween the insulators 252 and 254. In a plasma doping apparatus, theions may be implanted in the workpiece 138 in a central area of the gapspacing due to the shape of the boundary 241 and the electric fieldlines within the plasma sheath 242. For instance, due to the differencein vertical spacing between the two insulators 252, 254, ions strike theworkpiece at a non-zero angle in the space (G7). In addition, few ionsstrike the workpiece proximate the insulators outside of space G7 inthis embodiment.

FIG. 16 is a plot 603 of the distribution of incident angles of ionsstriking the workpiece 138 consistent with the illustrated iontrajectories of FIG. 15. As shown, the plot 603 reveals the incidentangles are centered about a non-zero center angle of about 45 degreeswith an angular distribution of about 20 degrees about this centerangle. In other embodiments, the center angle can vary between −80 to+80 degrees and the angular distribution about the center angle may varyfrom about +20 to −20 degrees. This range of incident angles enablesconformal doping of three dimensional structures.

By varying the gap width (δ), the spacing between the insulators (Z2-Z1)and the position of the insulators with respect to the workpiece (Z1),the center angle and angular distribution can be modified to achieve awide range of values, including, but not limited to, large center angles(i.e. >60°) with small angular distributions (i.e. <5°), large centerangles (i.e. >60°) with large angular distributions (i.e. >10°), smallcenter angles (i.e. <40°) with large angular distributions (i.e. >10°),and small center angles (<40°) with small angular distributions (<5°).

Turning to FIG. 17, a block diagram of another embodiment consistentwith the present disclosure is illustrated where the vertical spacings(Z1,Z2) between an insulating modifier and the plane 151 defined by thefront surface of the workpiece 138 may be adjusted. The insulatingmodifier may be the insulators 252 and 254 as detailed in otherembodiments. An actuators 703 a,b may be mechanically coupled to theinsulators 252 and 254, respectively to drive the insulators in avertical direction as shown by arrows 730, 732 relative to the plane151. The Z positions of the insulators 252 and 254 relative to the plane151, and also relative to each other, influence the shape of theboundary between the plasma and the plasma sheath and also thetrajectories of the ions striking the workpiece 138. The actuators 703a,b may be controlled by controllers, such as controllers 356 a,b. Inother embodiments, a single controller is used to control both actuators703 a,b.

FIGS. 18 and 19 are cross sectional views consistent with FIG. 17 toillustrate ion trajectories at differing Z positions of the insulators252 and 254 relative to the plane 151 with all other parameters beingequal. In FIG. 18, the insulators 252, 254 are vertically spaced by adistance of (Z2 a-Z1). In FIG. 19, the insulators 252, 254 arepositioned using a second vertical spacing (Z2 b-Z1), where Z2 b>Z2 a.Therefore, the gap angle (ψ) is greater in FIG. 19. In FIG. 18, theboundary 863 between the plasma and the plasma sheath has a roughlyconvex shape relative to the plane 151. In contrast, in FIG. 19, theboundary 963 has a shallower shape. The shape of the boundaries 863, 963combined with the Z gap distances (Z1) and (Z2 a,Z2 b), the gap angle(ψ), and the electric field lines in the plasma sheath, influences thecenter angle of the ions striking the workpiece 138. For example, thecenter angle of ions striking the workpiece 138 with the relativelyshort vertical spacing (smaller gap angle) is closer to zero degrees(i.e. closer to striking the workpiece at a perpendicular angle) thanthe center angle of ions striking the workpiece 138 with the relativelygreater vertical spacing (larger gap angle) shown in FIG. 19.

In another embodiment, the vertical spacing between the insulators(Z2-Z1) is maintained, while Z1 is varied. This has the effect of movingthe insulators closer (or further) from the workpiece, while maintainingthe gap angle (ψ). In this embodiment, the center angle remainsconstant, while the angular distribution varies as Z1 varies. In someembodiments, the angular distribution increases as Z1 is decreased,while the distribution decreases as Z1 is increased. In other words, forexample, one value of Z1 may result in an angular distribution of 5-10°about the center angle, while a smaller value of Z1 may result in anangular distribution of 20-30°. This effect may be due to the change inthe shape of the boundary between the plasma and the plasma sheath,which varies as the insulators are moved relative to the workpiece.

Turning to FIG. 20, a block diagram of another embodiment consistentwith the present disclosure is illustrated where the horizontal spacing(G) between insulators 252 and 254 may be adjusted. The horizontalspacing adjustments may be in lieu of, or in addition to, the earlierdetailed vertical spacing adjustments of FIGS. 18 and 19. An actuator912 may be mechanically coupled to at least one of the insulators 252and 254 to drive the insulators in the direction shown by the arrow 916relative to one another. The actuator 912 may be controlled by acontroller such as controller 356. Modification of the horizontalspacing (G) affects both the gap width (δ) and the gap angle (ψ).

In one embodiment, the horizontal gap spacing (G) between the insulatorsis varied. Modification of the horizontal gap spacing can be used toaffect both the center angle and the angular distribution. For example,if the horizontal gap spacing is reduced to 0 or made negative by havingthe insulators overlap, as shown in FIG. 21, the center angle can bemade very large. Small positive horizontal gap spacings will result inlarge gap angles (ψ), depending on the values of Z2 and Z1, resulting inlarger center angles. Large positive horizontal gap spacings will reducethe gap angle (ψ), resulting in a smaller center angle.

A bimodal angular spread 1200, such as that shown in FIG. 23, can becreated using the configuration shown in FIG. 22. A bimodal angularspread refers to a first center angle having a first angulardistribution and a second center angle having a second angulardistribution. Such a bimodal angular spread may also be created bychanging the relative vertical position of only two insulators such asillustrated in FIG. 15. In the embodiment of FIG. 22, at least threeinsulators 1400, 1402, 1404 are used. By arranging the outer twoinsulators 1400, 1404 on the same vertical plane (Z2), and maintainingthe same horizontal spacing G8, G9 between the insulators, it ispossible to create a symmetric bimodal angular spread 1200, centeredabout +/−θ°. As described above, the center angles can be modified byvarying the vertical spacing between the outer insulators 1400, 1404 andthe middle insulator 1402, so as to vary the gap angles (ψ). The angularspread can be modified by varying the horizontal spacing (G8, G9)between the insulators 1400, 1402, 1404, so as to vary the gap width(δ). An asymmetric distribution can be created by making Z2 a differentthan Z2 b, by choosing G8 different than G9, or a combination of bothactions.

While the previous embodiments show the insulators as being planar, thisis not a requirement of the disclosure. FIG. 24 a-c shows several otherembodiments of the insulators. FIG. 24 a shows an inverted “V” shapedinsulator configuration. As described above, the plasma sheath followsthe shape of the insulator. Therefore, the sheath forms a correspondinginverted “V” shape. Gaps in the insulator 1500 allow ions to passthrough the insulator. The slope of the inverted “V”, as defined by φ,defines the center angle of the ion distribution. The gap angle (ψ) inthis embodiment would be the complement of φ. The gaps Gc, Gd define theangular spread α1, α2, respectively. As can be seen when FIG. 24 a andFIG. 24 b are compared, a larger gap width (such as Gc) allows a greaterangular spread than the narrower gap width Gd (i.e. α1>α2). FIG. 24 cillustrates another embodiment, in which the insulator 1502 isnon-linear, curved or curvilinear, such that the gap width Ge is at anangle to the workpiece 138. As explained above, the gap angles determinethe center angle, while the widths of the gaps determine the angularspread.

Other embodiments are also possible and within the scope of thedisclosure. For example, in some embodiments, two or more insulators areused, where they are spaced apart so as to create a gap between them.This gap between the insulators allows ions to pass through to aworkpiece. In other embodiments, a single insulator is used, which hasat least one opening or gap in it, through which ions may pass.

There are several considerations when developing a system. A higher gapangle (ψ) results in a greater center angle of the ion distribution. Thelength of the opening along plane 257 defines the width of the gap (δ).The gap width (δ) affects the angular spread of the ion distribution. Itis important to note that these two variables are independent of oneanother. In other words, the gap angle (ψ) can be modified withoutchanging the gap width (δ). Similarly, the gap width (δ) can be changedwithout affecting the gap angle (ψ). Another variable of interest is thedistance from the gap (or either insulator) to the workpiece 138. Again,this variable can be changed independent of the other two variables. Useof independent horizontal and vertical actuators (see FIGS. 17 and 20)allow maximum flexibility in determining these parameters.

FIG. 25 is a block diagram of a plasma processing apparatus 1600 havinga scanning system 1602 to drive an insulating modifier 248 relative theworkpiece 138. In the embodiment of FIG. 25, the insulating modifier 248includes square insulating sheets 1612 and 1614 that are best seen inFIG. 26. The scanning system 1602 may include one or more actuators 1604mechanically coupled to the insulating sheets 1612 and 1614 to drive thesame in both the vertical and horizontal directions. The actuator 1604may be controlled by a controller such as controller 356.

FIG. 26 is plan view of the square insulating sheets 1612 and 1614 and adisk shaped workpiece 138 to illustrate one example of relative movementbetween the same. In the embodiment of FIG. 26, the scanning system 1602may drive the square insulating sheets 1612 and 1614 from Position A, toPosition B, and Position C, etc. so that all portions of the workpiece138 are exposed to the gap defined by the square insulating sheets 1612and 1614. If a Cartesian coordinate system is defined as detailed inFIG. 26, the insulating sheets 1612 and 1614 are driven in the Xdirection of FIG. 26. In other embodiments, the insulating sheets 1612and 1614 or another set of different insulating sheets may be driven inthe Y direction or any angle between the X and Y directions. Inaddition, the workpiece 138 may be rotated as the scanning system 1602drives the insulating sheets 1612 and 1614 in one direction. Theworkpiece 138 may also be rotated by a predetermined rotation angleafter the scanning system 1602 drives the insulating sheets in onedirection. In one example, the rotation may be about a central axis ofthe workpiece as illustrated by arrow 1624.

Although the scanning system of FIG. 25 is shown with two insulatingplates at a vertical spacing from one another, other embodiments arepossible. For example, the scanning system can be made using threeinsulating plates, thereby creating two gaps, as shown in FIG. 22.Additionally, the alternate shapes, such as those shown in FIG. 24 canbe used in the scanning system. Furthermore, the patterns shown in thesefigures can be replicated, such that there are multiple gaps across thewidth or length of the workpiece. In some embodiments, all gaps producethe same angular distribution (as shown in FIG. 15-16). In otherembodiments, the gaps produce opposite distributions at +/−θ° (as shownin FIG. 22-23). In other embodiments, the gaps are used to producevaried angular distributions. In this embodiment, the final angulardistribution experienced by the workpiece would be the sum of thevarious angular distributions.

Turning to FIG. 27, a scanning system 1602 consistent with FIG. 25 isillustrated. Compared to FIG. 25, the scanning system 1602 of FIG. 27includes a plurality of insulators 1702-1, 1702-2, 1702-3, . . .1702-(n−1), and 1702-n that define a plurality of gaps there between1703-1, 1703-2, . . . 1703-n. The scanning system may drive theplurality of insulators 1702-1, 1702-2, 1702-3, . . . 1702-(n−1), and1702-n relative to the workpiece 138 so the plurality of gaps 1703-1,1703-2, . . . 1703-n pass over the workpiece 138.

Modification of the gap angle (ψ) can be done by varying the gapspacing, or by varying the vertical spacing (Z2-Z1). Changes to gapangle may affect the center angle. Modification of the angulardistribution can be done by varying the height of the insulators (Z1) orby changing the gap spacing. Modifications to all three parameters (Z2,Z1 and gap spacing) can be employed to create a desired center anglewith a desired angular distribution or spread.

In addition, it may be beneficial or advantageous to cool the insulators252 and 254. In some embodiments, these insulators may have channelsembedded in them, whereby fluid, such as liquid or gas, may passthrough, to remove heat. In other embodiments, the insulators may begood thermal conductors and may be in contact with a thermal sink.

As mentioned above, the sheath modification can be used to perform avariety of plasma processing steps. For example, a deposition or etchprocess can utilize these techniques. For instance, with respect todeposition, it is often necessary in semiconductor processing to deposita conformal (i.e. equal thickness) film in a high aspect ratio gap.

In this processing, material from the plasma is deposited on the surfaceof the workpiece, thereby creating a film atop the workpiece. This canbe done a plurality of times to create varying film thicknesses. Threedimensional features are more difficult to deposit upon, as the surfacesof the feature may be vertical with respect to the top surface of theworkpiece. Greater aspect ratios are even more difficult to depositupon. An aspect ratio is defined as the depth (or height) of aparticular feature, such as a spacer or trench, divided by its width. Asdevice geometries shrink, void-free filling of high aspect ratio spaces(where high aspect ratio is defined to be greater than 3.0:1) becomesincreasingly difficult due to limitations in existing depositionprocesses.

The formation of liners in trenches and spacers are examples of suchdifficult processes. A major challenge for integrating low dielectricconstant films into copper damascene stacks is sealing the interfacebetween the porous dielectric film and the conducting copper diffusionbarrier at the trenches, especially the sidewalls.

Plasma Enhanced Chemical Vapor Deposition (PECVD) is one possibleprocess that can be used to form these liners. However, the performanceof line-of-sight processes is limited by the aspect ratio of the threedimensional feature. As aspect ratios increase, coverage and thereforeperformance of the sealing process decreases.

Lining trenches is but one example of a plasma process that requiresmodification to traditional PECVD processes. Deposition of doped (i.e.boron or phosphorus doped) silicon films to form three-dimensionaldevices is another example. Formation of air gaps at the interconnectlevels is yet another example.

FIGS. 28 b-c show a variety of three dimensional features, which can beconformally deposited using the PECVD process described in thisdisclosure. FIG. 28 a shows a conventional flat workpiece surface. Sucha surface is best deposited with ions or neutrals, all of which areperpendicular or nearly perpendicular to the surface of the workpiece.FIG. 29 a shows the ion angular distribution of the optimal deposition.Such a deposition is done without any modification of the plasma sheath.

FIG. 28 b shows a narrow, deep trench compared to the trench of FIG. 28c. This trench has a left sidewall 1720, a right sidewall 1722 and abottom surface 1724. A uniform coating or layer 1726 is applied to thesurface of the substrate, including the substrate surface 1728, thesidewalls 1720, 1722 and the bottom surface 1724. Clearly, an incidentbeam which is only perpendicular to the substrate surface 1728 can onlybe used to coat the substrate surface 1728 and the bottom surface 1724.The angle of incidence is defined with respect to a line perpendicularto the workpiece plane 151. Thus, an angle of incidence of 0° isperpendicular to the workpiece plane 151. Trajectory 1730 has an angleof incidence of 0°, while trajectory 1732 has a greater angle ofincidence than trajectory 1734. Trajectory 1734 is shown having an angleof incidence of θ₁°

To properly and uniformly deposit material on the sidewalls, it isnecessary to have a modified ion angular distribution. The ions havingan angle of incidence of 0° (trajectory 1730) deposit material on thesubstrate surface 1726 and bottom surface 1728. Ions having an angle ofgreater than a particular value (such as those traveling alongtrajectory 1732) can deposit material only on the upper of the sidewalls1720, 1724, as the top surface 1728 casts a shadow which stops ions fromreaching the lower portions of the sidewalls. Ions with an angle ofincidence 1734 less than this particular value are able to depositmaterial on all portions of the sidewalls 7120, 1722. Thus, if the depthof the feature is represented by the variable, d, and the width of thefeature is represented by the variable w, the maximum angle ofincidence, θ₁, capable of depositing material on the bottom portion ofthe sidewall is defined by:

tan θ₁ =w/d, or θ₁=arctan(w/d)

Angles greater than 01 can only deposit material on a portion of thesidewall, thereby creating an uneven layer of material.

FIG. 30 a shows the feature of FIG. 28 b. Various points (Q-Z) arelabeled on the workpiece and within the feature. For example, Q,R,S areon the workpiece to the left of the feature, while points X,Y,Z are onthe workpiece to the right of the feature. Points T,W are along thesidewalls of the feature, and points U,V are on the bottom surface ofthe feature.

FIGS. 30 b-f show various timing diagrams. It is assuming that the gapdescribed above is scanned relative to the workpiece, such that the gapis moving from the left to the right of the feature (as shown in FIG. 30a). Each timing diagram shows the height that is being deposited as afunction of time.

For example, FIG. 30 b shows the timing diagram when an angle ofincidence of 0° is used. In this embodiment, the material is depositedalong the surface of the workpiece as the gap moves to the right. Oncethe opening is directly above the feature (i.e. point S), the depth ofthe deposition changes, corresponding to the bottom of the feature. Whenthe gap is directly above point X, the height changes again, as thedeposition now occurs on the surface of the workpiece. Notice that thesidewalls cannot be deposited using an angle of incidence of 0°.

FIG. 30 c shows a timing diagram for an angle of incidence less than θ₁(defined as arctan (w/d)). In this figure, the ions reach a portion ofthe workpiece to the left of the gap. In other words, when the gap isdirectly over point S, the ions are targeted toward a point between Rand S. Therefore, the first portion of FIG. 30 c is a delayed version ofFIG. 30 b. When the gap reaches a point where the ions contact point S,further lateral movement of the gap will cause the ions to strike theleft sidewall, reaching points T and U. Since the angle of incidence isless than θ₁, the entire sidewall is deposited. As the gap continues tomove to the right, eventually the ions cannot deposit the feature, asthe workpiece surface (i.e. point X) blocks the ions. At this point, theions continue to deposit on the top surface of the workpiece, again as adelayed version of FIG. 30 b. Since the ions are angled to the left, theright sidewall is never deposited.

FIG. 30 d shows a timing diagram for an angle of incidence greater thanθ₁. This diagram closely resembles FIG. 30 c with several importantdifferences. First, the diagram is further delayed with respect to thetop surface (i.e. Q,R,S,X,Y,Z). Also, due to the increased angle ofincidence, the ions cannot reach the bottom of the feature (point U)before being blocked by the top surface (point X). As a result, thebottom surface and the right sidewall are not deposited.

FIG. 30 e shows a timing diagram for an angle of incidence that isnegative, but greater than −θ₁. This figure corresponds to FIG. 30 c, inthat the ions reach the entire sidewall and also a portion of the bottomof the feature. Since the ions are directly downward and to the right,the right sidewall is deposited, but the left sidewall is not.

FIG. 30 f shows the timing diagram for an angle of incidence that ismore negative than −θ₁. This figure shows that the ions never reach thebottom surface of the feature, and only are deposited on a portion ofthe right sidewall.

By choosing the correct range for the angle of incidence, it is possibleto create the desired deposition of a three dimensional feature. Thediagrams of FIG. 30 b-f are examples and the locations of the points Q-Zare only intended to illustrate the effects of changing the angle ofincidence.

FIG. 28 c shows a wide, shallow trench compared to FIG. 28 b. Thistrench has a left sidewall 1740, a right sidewall 1742 and a bottomsurface 1744. A uniform coating or layer 1746 is applied to the surfaceof the substrate, including the substrate surface 1748, the sidewalls1740, 1742 and the bottom surface 1744. As below, to properly anduniformly deposit material on the sidewalls, it is necessary to have amodified ion angular distribution. The ions having an incident angle of0° (those traveling along trajectory 1750) deposit material on thesubstrate and bottom surfaces. Ions having an incident angle greaterthan about 70°, such as those ions following trajectory 1752 can depositmaterial only on the upper portions of the sidewalls 1740, 1742, as thetop surface 1728 casts a shadow which stops ions from reaching the lowerportions of the sidewalls. Ions with a relatively smaller angle ofincidence, e.g., those following trajectory 1754 are able to depositmaterial on all portions of the sidewalls 1740, 1742 and on the bottomsurface 1744. Thus, if the depth of the feature is represented by thevariable, d, and the width of the feature is represented by the variablew, the maximum incident angle θ₂, capable of depositing material on thebottom portion of the sidewall is defined by:

tan θ₂ =w/d, or θ₂=arctan(w/d)

In this case, the width (w) is much greater than the depth (d),therefore θ₂>θ₁ (FIG. 28 b). In one embodiment, θ₁ may be 30°, while θ₂may be 50°. Thus, a wider ion angular distribution may be used.

In all cases, the maximum desired ion angular distribution is related tothe aspect ratio of the three dimensional feature to be deposited.Narrow, deep features require a smaller range of angular distribution asshown in FIG. 29 b, while wide, shallow features can utilize a broaderrange of angular distribution, as shown in FIG. 29 c.

Thus, the disclosed embodiments can be utilized to produce conformaldeposition of three dimensional features. The plasma sheath ismanipulated to create an ion angular distribution in accordance withFIG. 29 b, where θ is defined based on the aspect ratio of the threedimensional feature to be deposited upon. As described with respect toFIGS. 4-5, the angle of incidence of incoming ions can be manipulated tocreate an angular distribution, centered around 0°, of +/−θ. In someembodiments, θ is based on arctangent (w/d) where w is the feature widthand d is defined as the feature depth. This is done by varying the sizeof the gap, and its vertical spacing from the workpiece, as shown inFIGS. 7-10.

In some embodiments, it may be desirable to deposit material in a threedimensional feature, while leaving an air gap beneath the deposition.FIG. 31 a shows a three-dimensional feature 1900, having sidewalls 1902,1904 and a bottom surface 1905. Material 1906 is deposited in such a wayso as to leave an air gap 1908 between the deposited material 906 andthe bottom surface 1905.

Such a configuration can be created by properly modifying the ionangular distribution. For example, based on the description above, it isclear that the incoming ions cannot have an incident angle perpendicularto the workpiece, as this would deposit material on all horizontalsurfaces, including bottom surface 905. Furthermore, ions having a lowangle of incidence are capable of reaching the bottom surface 1905 andthe lower portions of the sidewalls 1902, 1904. Thus, to achieve thedesired pattern, a different angular distribution is required, as shownin FIG. 31 b. The angle distribution is bimodal, centered about −θ° andθ°. As before, the preferred angular distribution is related to theaspect ratio of the feature 1900. In this case, assume that the depth ofthe feature is d and its width is w. Further assume that the height ofthe desired air gap 1908 is given by h. The angle of incidence cannot beless than that defined by:

tan(θ₃)=w/(d−h), or θ₃=arctan(w/(d−h)).

FIG. 31 b shows a bimodal angular distribution which would achieve thepattern shown in FIG. 31 a. Insulators disposed in the configurationshown in FIG. 22 can be used to create this bimodal angulardistribution.

As described above, the plasma sheath can be manipulated to vary itsshape. While the above disclosure suggests use of a time invariantangular distribution, based on a specific sheath shape, the disclosureis not limited in this way. For example, as material is deposited on thetwo sidewalls, the width of the feature decreases at a higher rate thanthe depth. Therefore, the aspect ratio of the feature increases. Thus,to counteract this effect, the sheath can be manipulated over time todecrease the angular distribution, based on the increased aspect ratio.

Thus, to conformally deposit a three dimensional feature, one may use anion angular distribution based on the initial aspect ratio, as describedabove. As material is deposited on the sidewalls and bottom surface, theaspect ratio necessarily increases. This requires a correspondingdecrease in the angular distribution. This process is repeated until thedesired amount of material has been deposited on the sidewalls and thebottom surface. As described above, the angular distribution is adjustedby varying the separation of the insulators 212, 214 (see FIG. 8) or thedistance between the insulators 212, 214 and the workpiece 138 (see FIG.10). This adjustment can be made continuously, based on the depositionrate, or can be made in discrete steps as required. In some embodiments,plasma parameters can be modified during the process. In otherembodiments, the implant energy can be modified during the process.

In another example, consider the feature shown in FIG. 31 a. Asdescribed above, a bimodal ion angular distribution is used to create alayer of material spaced above the bottom surface. The center angles ofthe bimodal distribution are related to the aspect ratio of the featureand the desired height of the air gap. Once that layer is formed, theangular distribution can be modified. For example, the two bimodalcenter angles can be decreased, to deposit more material on top of theprevious deposited material. This process can continue until the centerangles reach 0°. This allows the feature to be filled as shown in FIG.31 a. In another embodiment, after the layer of material has beendeposited and the air gap 908 is formed, a traditional angle ofincidence of 0° can be used to layer more material onto the previouslydeposited layers.

Furthermore, this method of using varying angles of incidence need notbe used only for conformal deposition. This process can be modified soas to create an uneven ion flux if desired. In addition, the use of adeposition based on a modified sheath shape can be combined with othersteps. For example, a traditional (orthogonal) deposition may precede orfollow the conformal deposition process described above. For example,the ion angular distribution shown in FIG. 31 b can be used to createthe air gap 1908 in the trench. A traditional orthogonal deposition maythen be subsequently employed to increase the thickness of the coating.Alternatively, the traditional PECVD may be applied first, followed by adirectional deposition.

This deposition method can be applied to a variety of films anddeposition precursors. For example, materials such as but not limited toorganosilicon precursors (methysilanes, hexamethyldisiloxane (HMDSO),octamethyltetrasiloxane (OMCTS), and tetramethyltetrasiloxane (TMCTS))can be used for deposition of SiCOH for pore sealing applications andformation of air gaps. SiH₄ can be used for deposition of SiO₂ and SiNlines and spacers. Organometallic precursors can be employed fordeposition of liners and diffusion barriers in vias and lines. Finally,SiH₄/B₂H₆/PH₃/AsH₃ mixtures can be used for three dimensionaldeposition.

In addition to deposition, manipulation of the plasma sheath can beemployed for etching processes as well. During plasma etching, ions andneutrals are created and controlled to affect the sidewall profile ofthe three-dimensional feature being etched. In some embodiments, astraight (i.e. vertical) sidewall is desired. This is performed using ananisotropic etch, wherein the ions are directed orthogonally to thesurface of the workpiece. Examples where this type of etching is usedinclude gate stack, BEOL damascene and FinFET. FIG. 32 a shows a feature2002 which is etched by orthogonally directed ions 2010. The portions ofthe substrate 2004 which are not to be etched are protected by a mask2000. As all ions are orthogonal to the surface of the substrate 2004,the etched region 2002 has vertical sidewalls. FIG. 29 a shows the ionangular distribution necessary to create this feature.

In other embodiments, an isotropic etch is desirable, and is typicallydone using wet chemistry (e.g. S/D etch prior to epi deposition forimproved overlap). In certain embodiments, it is desirable to havetrenches or other three-dimensional features where the sidewalls are notvertical, but rather are tapered. FIG. 32 b shows such a feature wherethe sidewalls are slightly tapered. Note that the increased iondistribution allows the sidewalls to be etched beneath the mask in thehorizontal direction.

In one embodiment, ions having a wide angular spread (such as greaterthan 40°, as shown in FIG. 29 c) are impacted on the workpiece 2024.This etches the workpiece 2024 in all areas not protected by a mask2020. Since a wide angular spread is used, the ions 2030 having thegreatest angle of incidence are able to etch material 2026 that ispositioned below the mask 2020. A small wedge 2028 of substrate remainsbeneath the mask, as it is protected by mask 2020. By increasing the ionangular spread (i.e. allowing a greater maximum angle of incidence), theamount of material 2026 under the mask that is etched can be increased,thereby increasing the degree of taper. As the material is etched away,the angular distribution is reduced, so that the maximum angles ofincidence are reduced. An example angular spread is shown in FIG. 29 b.The decrease in angular spread tends to focus the etching on a narrowerarea. As the process continues, the angular spread can continuouslyreduced, until it becomes the traditional spread, such in FIG. 29 a. Therate at which the angular spread is varied with time determines thesidewall shape. The taper 2031 is based partly on the initial angularspread and the rate at which the angular spread is decreased. A slowdecrease in angular spread yields a feature having a slight taper 2031.A more rapid decrease in angular spread increases the taper of thefeature.

As explained, the tapered effect shown in FIG. 32 b can be created usingthis method. Additional shapes, such as those shown in FIGS. 32 c and 32d, can also be created by using an angular distribution, centered around0°, and varying the angular spread as a function of time. To create theshape shown in FIG. 32 b, the process begins by using a wide angle. Thisangle etches material near the top of the sidewalls. As the trenchdeepens, the angular spread is reduced, which causes the resultingsidewalls to become tapered. FIG. 32 c uses a similar profile as used tocreate the feature of FIG. 32 b, however the duration of the ion beamhaving an angle of incidence of 0° (see FIG. 29 a) is reduced, ascompared to the duration of this ion beam when used to create theprofile shown in FIG. 32 b. Furthermore, the starting angulardistribution is greater than that used to create the shape shown in FIG.32 b. The feature of FIG. 32 d is created using a wide angular spread,such as greater than 40°, as shown in FIG. 29 c, with little or noreduction in angular spread over time.

FIG. 33 a show a three dimensional feature 2100 in which the taper ofthe sidewalls 2102 is greater than 90 degrees. 90 degrees is defined asvertical to the surface of the workpiece. Tapers greater than 90 degreesimply that the feature increases in width as the depth increases. Toetch the feature 2100 in this manner, an ion angular distribution, asshown in FIG. 31 b may be used. The bimodal nature of the incident ionscreates two etched regions 2104, 2106, each of which is roughly parallelto one of the center angles of incidence. In FIG. 33 a, the angle ofincidence is sufficiently large such that a portion 2110 of the bottomsurface of the feature 2100 is not completely etched. The size of thisremaining portion 2110 is a function of the incidence angle, the widthof the opening in the mask 2112, and the depth of the feature 2100.

For example, the innermost edges of the etched region are defined as thefirst portion of the substrate which has a line-of-sight to the ionbeam. These positions are designated as φ1 and φ2. φ1 is offset from theright corner of the mask by a distance equal to d*tan(θ), where d is thedepth of the feature 2100 and θ is the angle of incidence. If theopening in the mask 2112 is given by w, then an unetched portion 2110will exist if d*tan(θ) is greater than w/2.

To eliminate this unetched portion 2110, a second angular distribution,centered at 0° or a traditional orthogonal distribution (see FIG. 29 a),can be employed after the bimodal ion angle distribution is complete.Such a feature can be seen in FIG. 33 b.

It could also be achieved by performing an over-etch step where a etchbarrier is used between two layers. In the etching process, there aredifferent selectivities between materials, such that some material willnot etch with the plasma used. Thus, the etching process will then stopat this layer.

Other feature shapes can be generated by combining the bimodal iondistribution, shown in FIG. 31 b, with an angular distribution, enteredaround 0° (such as those shown in FIGS. 29 a, 29 b and 29 c). FIGS. 33 cand 33 d show two feature shapes that can be created by modifying theangular distribution with time, so that it may utilize both a 0°centered angular distribution and a bimodal angular distribution. Forexample, the shape in FIG. 33 c can be created by starting with an etchhaving no angular spread (see FIG. 29 a). This creates a verticaltrench, as is known in the art. Later, a wide angular spread is used,which etches material so as to form the desired shape. The shape shownin FIG. 33 d can be created using isotropic etching.

The terms “angle of incidence” and “incident angle” are usedinterchangeable throughout this disclosure, and have the same meaning.Specifically, the angle of incidence is the angle at which ions strikethe workpiece. It is measured as a deviation from a line that isperpendicular to the plane 151 defined by the front surface of theworkpiece. In other words, ions that strike the workpieceperpendicularly have an angle of incidence or incident angle of 0°.

Accordingly, there is provided methods of performing plasma processingon a feature on a workpiece. In certain embodiments, the shape of theplasma sheath is modified and then material from the plasma is depositedon the feature. In a further embodiment, the modification of the plasmasheath varies in relation to the aspect ratio of the feature. In stillother embodiments, the modification of the plasma sheath also variesover time, as material is deposited on the feature. Modification of theplasma sheath can also be used to perform etching of a workpiece.Various modifications of the plasma sheath can be performed to vary theshape and profile of the etched feature.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Further, although the present disclosure hasbeen described herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art will recognize that its usefulness is not limited thereto andthat the present disclosure may be beneficially implemented in anynumber of environments for any number of purposes. Accordingly, theclaims set forth below should be construed in view of the full breadthand spirit of the present disclosure as described herein.

What is claimed is:
 1. A method of etching a three dimensional feature,having a desired width, depth and taper, in a workpiece, comprising:generating a plasma having a plasma sheath adjacent to a front surfaceof the workpiece; and modifying a shape of a boundary between the plasmaand the plasma sheath while accelerating material from the plasma acrossthe boundary to etch the three dimensional feature on the front surfaceof the workpiece.
 2. The method of claim 1, wherein the material strikesthe three dimensional feature at a range of incident angles, and whereinthe range of incident angles is dependent on the shape of the boundarybetween the plasma and the plasma sheath.
 3. The method of claim 2,wherein the range of incident angles includes a center angle and adistribution about the center angle.
 4. The method of claim 3, whereinthe three dimensional feature is inwardly tapered, such that its desiredwidth at the front surface of the workpiece is greater than its desiredwidth at a bottom of the three dimensional feature, and the center angleis perpendicular to a plane defined by the front surface of theworkpiece and the distribution is greater than zero degrees.
 5. Themethod of claim 3, wherein the three dimensional feature is outwardlytapered, such that its desired width at the front surface of theworkpiece is less than its desired width at a bottom of the threedimensional feature, and the range of incident angles comprises twocenter angles, each having a distribution.
 6. The method of claim 3,wherein the modification of the boundary comprises: selecting a firstcenter angle and a first distribution based on the desired taper; anddirecting material toward the three dimensional feature using the firstcenter angle and the first distribution, whereby the material etches theworkpiece to a first depth.
 7. The method of claim 6, furthercomprising: selecting a second center angle and a second distributionbased on the desired taper and the first depth; and directing materialtoward the three dimensional feature using the second center angle anddistribution, whereby the material etches the workpiece to a seconddepth.
 8. The method of claim 7, further comprising repeating theselecting and directing steps a plurality of times until a desired depthhas been etched.
 9. The method of claim 8, wherein the distribution isreduced over time.
 10. The method of claim 8, wherein the incident angleis reduced over time.